RE: [PATCH iwl-net 09/10] idpf: add support for Rx timestamping

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Olech, Milena wrote:
> On 11/14/2024 9:54 PM, Willem de Bruijn wrote:
> 
> > Milena Olech wrote:
> > > Add Rx timestamp function when the Rx timestamp value is read directly 
> > > from the Rx descriptor. Add supported Rx timestamp modes.
> > > 
> > > Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>
> > > Signed-off-by: Milena Olech <milena.olech@intel.com>
> > > ---
> > >  drivers/net/ethernet/intel/idpf/idpf_ptp.c  | 74 
> > > ++++++++++++++++++++-  drivers/net/ethernet/intel/idpf/idpf_txrx.c | 
> > > 30 +++++++++  drivers/net/ethernet/intel/idpf/idpf_txrx.h |  7 +-
> > >  3 files changed, 109 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/net/ethernet/intel/idpf/idpf_ptp.c 
> > > b/drivers/net/ethernet/intel/idpf/idpf_ptp.c
> > > index f34642d10768..f9f7613f2a6d 100644
> > > --- a/drivers/net/ethernet/intel/idpf/idpf_ptp.c
> > > +++ b/drivers/net/ethernet/intel/idpf/idpf_ptp.c
> > > @@ -317,12 +317,41 @@ static int idpf_ptp_gettimex64(struct ptp_clock_info *info,
> > >  	return 0;
> > >  }
> > >
> > > +/**
> > > + * idpf_ptp_update_phctime_rxq_grp - Update the cached PHC time for a given Rx
> > > + *				     queue group.
> > 
> > Why does each receive group have a separate cached value?
> > They're all caches of the same device clock.
> 
> That's correct - they all caches values of the same PHC, however I would
> like to have an effective method to access this value in hotpath where
> I'm extending the Rx timestamp value to 64 bit.
> 
> For the same reason I cached Tx timestamp caps in
> idpf_vport_init_fast_path_txqs.

Oh to avoid reading a cold cacheline in the hot path. Okay, that makes
sense. Please make a note of this in the commit message.